System and method for heating and forming thermoplastic material

Abstract

A system and method for heating thermoplastic material and forming elongated and involute thermoplastic articles from the thermoplastic material is disclosed. Means are provided for controllably heating a sheet of thermoplastic material to form preselected temperature gradients throughout the sheet of thermoplastic material. Means are further provided for planarly supporting the heated sheet of thermoplastic material allowing for transverse motion of the heated sheet of thermoplastic material at the center thereof and further allowing for controlled slippage of the heated sheet of thermoplastic material toward said center thereof relative to the planar support means. Means are also provided for transversely forming a heated sheet of thermoplastic material into the shape of an elongated or involute plastic article.

What is claimed is: 
     
       1. A method of heating thermoplastic material to allow for subsequent forming of said material, said method comprising the steps of placing the thermoplastic material in an oven between opposing arrays of infrared heating elements each having reflector means located behind the respective heating elements relative to the thermoplastic material to reflect radiation from each said array toward the thermoplastic material, heating the thermoplastic material with the infrared heating elements, sensing the temperature of said reflector means, and controlling the temperature of said reflector means by simultaneously drawing air from outside the oven into the oven, venting heated air from the oven, and controlling said venting to maintain the reflector means at a substantially constant temperature to control the heating of said thermoplastic material. 
     
     
       2. A method as recited in claim 1 wherein the thermoplastic material comprises a sheet of said material and additionally comprising the step of rotating the sheet of thermoplastic material within said oven during said heating to heat said sheet of thermoplastic material in a concentrically uniform manner. 
     
     
       3. A method as recited in claim 1 wherein the thermoplastic material comprises a sheet of said material and additionally comprising the steps of planarly supporting the heated sheet of thermoplastic material so as to permit transverse movement of the center of said heated sheet of thermoplastic material radially inwardly towards the center thereof, transversely extending the center of the heated sheet of thermoplastic material into the interior of an involute female mold to form such sheet into an elongated conical shape piece, and pressurizing the interior cavity of the elongate conical sheet of thermoplastic material without substantially reheating said material to expand and press the thermoplastic material against the interior surface of the involute female mold. 
     
     
       4. A method as recited in claim 2 and additionally comprising the step of dividing the oven into two sections, each said section including a respective array of heating elements and its associated reflector means, and wherein said controlling the temperature of said reflector means includes simultaneously controlling the temperature of each said reflector means independently to control the heating of said thermoplastic material in each said section. 
     
     
       5. A method as recited in claim 1 wherein said controlling step comprises controlling the temperature of said reflector means so that said temperature is approximately equal to the minimum forming temperature of said material. 
     
     
       6. A method of heating thermoplastic material to allow for subsequent forming of said material, said method comprising the steps of placing the thermoplastic material in an oven between opposing arrays of infrared heating elements each having reflector means located behind the respective heating elements relative to the thermoplastic material to reflect radiation from each array toward the thermoplastic material, dividing the oven into two sections on respective sides of the thermoplastic material so that the thermoplastic material is exposed to both said sections, each section including a respective array of heating elements and its associated reflector means, heating the thermoplastic material by irradiating said material by both the infrared heating elements in combination, independently sensing the temperature of each said reflector means, and controlling the temperature of the reflector means in each said section by simultaneously drawing air from outside the oven into each section of the oven, venting heated air from each section of the oven, and controlling said venting from each said section responsively to the temperature of the reflector means in said sections to maintain the respective reflector means at a substantially constant temperature to control the heating of said thermoplastic material. 
     
     
       7. A method as recited in claim 6 wherein said controlling step comprises controlling the temperature of said reflector means in each said section so that said temperature is approximately equal to the minimum forming temperature of said material.